The present invention generally relates to an ultrasonic motor, and more particularly, to an ultrasonic motor driven by ultrasonic vibration.
Conventional types of ultrasonic motors using vibration have been proposed as described in, Japanese Patent Laid-Open Nos. 58-93477, 59-122385 and 60-51478 and Japanese Patent Publication 59-37673. The Japanese Patent Laid-Open No. 58-93477 discloses a method for arbitrarily switching the driving direction of a piezoelectric motor as required by applying a voltage output having the prescribed phase difference to a plurality of vibrators. Japanese Patent Laid-Open No. 59-122385 discloses a method for converting strong vibration energy of a supersonic wave into rotational or linear movement. This is accomplished by utilizing traveling waves combined with lateral waves and longitudinal waves excited on the surface of an elastic material. Japanese Laid-Open No. 60-51478 discloses a motor which displays accurate time by etching a pattern of 60 divisions of an electronic timepiece made of a piezoelectric motor. In this manner, the pattern detects the rotating state to control the drive of the motor.
The above ultrasonic motors have been satisfactory. However, the embodiments set forth above continuously rotate or rotate only when the driving voltage poorly formed driving wave shapes are input to the motor. Therefore, it is necessary to use a feedback control system of the conventional ultrasonic motor to control the RPM, stop positions and rotational speed. Hence, the system requires a control circuit resulting in the complication of the entire control system of the ultrasonic motor.
Accordingly, it is desirable to provide an ultrasonic motor which overcomes the shortcomings of the prior art.